The research proposed in this application is carried out with the objective of obtaining basic information on the effect of sphingomyelin on biological membrane structure and properties and how these effects might be related to aging and atherosclerosis in blood vessels. The work outlined will utilize three systems, liposome dispersions, planar bilayers and monolayers formed at an air/water interface. Liposomes will be used to study both compositional asymmetry between opposite bilayer faces and compositional domains within the planes of the bilayer in sphingomyelin-phosphatidylcholine- cholesterol systems. Studies of bilayer permeability and structure as functions of composition and temperature will be undertaken in systems exhibiting compositional domains. Details of the interactions between these three lipids will be examined directly using monolayer techniques. Preliminary studies of interactions between these bilayer systems and the apo peptides of alpha and beta lipoprotein will also be undertaken. In addition, permeability and transport properties, together with membrane fluidity will be studied in mammalian erythrocyte membranes obtained from a series of species exhibiting differences in the ratio of sphingomyelin to phosphatidylcholine. BIBLIOGRAPHIC REFERENCES: G. W. Stubbs, Burton J. Litman and Y. Barenholz, "Microviscosity of the Hydrocarbon Region of the Bovine Retinal Rod Outer Segment Disk Membrane Determined by Fluorescent Probe Measurements," Biochemistry 15, 2766 (1976). Y. Barenholz, J. Suurkuusk, D. Mountcastle, T. E. Thompson and R. L. Biltonen, "A Calorimetric Study of the Thermotropic Behavior of Aqueous Dispersions of Natural and Synthetic Sphingomyelins," Biochemistry 15, 2441 (1976).